Strings are used for debug instructions.

Bug: b/145351270
Change-Id: I6bc711c6c8b320bef6e5abbe9c4bda189fdafc0b
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/39884Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>